This invention relates to power converters, and more particularly to power converters having a three phase ac input and requiring power factor correction. This invention also relates to control of the input current and frequency of free-wheeling power sources, dc to three phase ac conversion and three phase ac to three phase ac power conversion, particularly when the frequencies differ.
Usually power factor correction is accomplished by monitoring the three input currents using three input current shunts or current transformers or the like. A sine wave current reference is also generated for each phase, often using the ac voltage inputs. The measured currents are compared to the current references and a feedback control pulse width modulates the input currents so that they conform to the current references.
The input stages are usually boost converters that boost the input to a high voltage storage capacitor. A buck converter may then convert the energy on the storage capacitor to a useful dc output. Upon application of the input power, large inrush currents occur. Present three phase power converters with power factor correction are notoriously sluggish in their response to transients.